LAMFAW 7.100 (Driver's Requested Lambda)

From Nefmoto

The function LAMFAW brings about an enrichment of the fuel-air mixture via lamfa_w when the driver demands maximum torque via mrfa_w. This then corresponds to the full-load enrichment. The intervention to the mixture via lamfa_w can be delayed via the delay time TLAFA. During turbocharger overboost, an additional enrichment is applied by a delta-lambda from the characteristic DLAMOB.

For the time TLAMFAS, an enrichment via the driver’s request as a function of altitude (LAMFAS) can be prevented (see sub-function LAMFADISABLE). Triggering of this time will be initiated if B_kh = true, LAMFA <1.0 and the altitude at which the function is disabled (as defined in LAMFAS) has been reached.

In this way, a reproducible driving cycle can also be achieved at higher altitudes.

In the sub-function LAMKR, an enrichment can be implemented during ignition angle intervention.

The sub-function LAMWL can be used for the enrichment during warm-up. If this procedure is used, tank-venting via the function LAMKO is not switched off.

In the sub-function LAMRLMIN, an enrichment via LAMRLMN is active for low loads (rl). This improves the combustion efficiency at low loads. If CWLAMFAW bit 2 is set, then the emergency fuel tank breather is disabled during lamrlmn-intervention.

Application Notes

A delay time TLAFA > 0 can only be applied when the mixture intervention via lamfa_w should be delayed.

The characteristic LAMFAS is not interpolated, which means that the characteristic initial value remains constant until a node is crossed.

For the fho-sample points of the characteristic LAMFAS, the following relationship applies: fho = 1
– altitude [m]/10,000 m

Since the variable fho has a quantization of 4/256 = 0.015625, this resolution must be considered when determining the switch-off. Similarly, there is a potential altitude deviation of ± 250 m because of the sensor tolerance.

For the calculation of the lower or upper threshold of fho, the following relationship applies for a nominal altitude cut-off threshold:

Lower altitude cut-off threshold:

fho [phys] = 1 – ((nominal altitude [m] – 250 m ) /10,000)

---> fho[Ink] = Integer (fho[phys]/0.015625) + 1Ink

---> fho upper limit [phys] = (1 – fho[Ink] x 0.015625)

---> Altitude upper limit = (1 – fho upper limit [phys]) x 10,000

Upper altitude cut-off threshold:

fho [phys] = 1 – ((nominal altitude [m] + 250 m)/10,000)

---> fho[Ink] = Integer (fho[phys]/0.015625)

---> fho lower limit [phys] = fho[Ink] x 0.015625

---> Altitude lower limit = (1 – fho lower limit [phys]) x 10,000

This produces the following values:

Nominal altitude

2,200 m

1,600 m

Altitude upper limit

2,500 m

1,875 m

The altitude upper limit is the fho lower limit!

fho lower limit

0.75

0.8125

Altitude lower limit

1,875 m

1,250 m

fho upper limit

0.8125

0.875

Thus, the characteristic LAMFAS is parameterized as follows for the nominal altitude of 2,200 m: